''Monjurosuchus'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
choristoderan reptile
Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...
that lived in what is now
China
China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...
and
Japan
Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
during the
Early Cretaceous
The Early Cretaceous ( geochronological name) or the Lower Cretaceous (chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma.
Geology
Pro ...
. It has large eyes, a rounded skull, robust legs with short claws, and a long, thin tail. Fossils have been found that preserve soft tissue, showing that it had soft skin and webbed feet.
Description and history
![Monjurosuchus](https://upload.wikimedia.org/wikipedia/commons/e/ed/Monjurosuchus.jpg)
''Monjurosuchus'' was first found in China as part of the Early Cretaceous
Jehol Biota
The Jehol Biota includes all the living organisms – the ecosystem – of northeastern China between 133 and 120 million years ago. This is the Lower Cretaceous ecosystem which left fossils in the Yixian Formation and Jiufotang Formation. These ...
. Named in 1940, the
type species
In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...
''M. splendens'' was the first reptile described from the
Yixian Formation
The Yixian Formation (; formerly transcribed as Yihsien Formation) is a geological formation in Jinzhou, Liaoning, People's Republic of China, that spans the late Barremian and early Aptian stages of the Early Cretaceous. It is known for its ex ...
. The
holotype
A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...
specimen was lost during
World War II
World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
but was replaced in 2000 by a recently discovered
neotype
In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...
preserving soft tissue.
In 2007, remains were described from the
Okurodani Formation
The Okurodani Formation is an Early Cretaceous geologic Formation (geology), formation in central Honshu, Japan. Part of the Tetori Group, it primarily consists of freshwater continental sediments deposited in a floodplain environment, with occasi ...
of the
Tetori Group of Japan. The Japanese material represents a different species of ''Monjurosuchus'' that has not yet been named.
''Monjurosuchus'' was a small choristodere, reaching a length of 40 cm with a 5 cm skull.
Unlike related choristoderes, ''Monjurosuchus'' has a relatively short neck with eight vertebrae, one less than usual. The skull is rounded rather than pointed and is dorsoventrally flattened in all fossils. The eye sockets are large and prominent temporal regions extend from the back of the skull. The jaws are lined with small, sharp teeth, while the
palate
The palate () is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity.
A similar structure is found in crocodilians, but in most other tetrapods, the oral and nasal cavities are not truly sepa ...
is covered in closely spaced tooth batteries.
[ One distinguishing feature of ''Monjurosuchus'' is the lack of a lower ]temporal fenestra
An infratemporal fenestra, also called the lateral temporal fenestra or simply temporal fenestra, is an opening in the skull behind the orbit in some animals. It is ventrally bordered by a zygomatic arch. An opening in front of the eye sockets ...
, a hole in the back of the skull that is common in many other diapsid
Diapsids ("two arches") are a clade of sauropsids, distinguished from more primitive eureptiles by the presence of two holes, known as temporal fenestrae, in each side of their skulls. The group first appeared about three hundred million years ago ...
reptiles, including most choristoderes. ''Monjurosuchus'' is also distinct in having small spikes on the edge of the squamosal The squamosal is a skull bone found in most reptiles, amphibians, and birds. In fishes, it is also called the pterotic bone.
In most tetrapods, the squamosal and quadratojugal The quadratojugal is a skull bone present in many vertebrates, including ...
bone at the back of the skull.
Specimens from China preserve soft tissue, including scales and webbing between the toes of the feet. The scales of ''Monjurosuchus'' were small, giving the animal soft skin. Two rows of larger scute
A scute or scutum (Latin: ''scutum''; plural: ''scuta'' "shield") is a bony external plate or scale overlaid with horn, as on the shell of a turtle, the skin of crocodilians, and the feet of birds. The term is also used to describe the anterior po ...
s run along its back. The rest of the scales on the back are small, while the scales on the underside are slightly smaller. The skin of ''Monjurosuchus'' has a similar appearance to the living Chinese crocodile lizard
The Chinese crocodile lizard (''Shinisaurus crocodilurus'') is a semiaquatic anguimorph lizard found only in cool forests in southeast China and northeast Vietnam. The Chinese crocodile lizard spends much of its time in shallow water or in over ...
''Shinisaurus''.[
The feet of ''Monjurosuchus'' are webbed, with skin covering all parts of the foot but the short claws. The limbs were robust and the hips are wide. The long, slender tail shows no adaptations for its presumed semi-aquatic lifestyle. ]Gastralia
Gastralia (singular gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In these ...
are present on the underside of ''Monjurosuchus'' and are much thinner than the ribs. Intestinal contents are preserved between the gastralia and ribs of one specimen. Most of the material is sediment, but there are also fragments of what may be arthropod cuticle
The cuticle forms the major part of the integument of the Arthropoda. It includes most of the material of the exoskeleton of the insects, Crustacea, Arachnida, and Myriapoda.
Morphology
In arthropods, the integument, the external "skin", or "s ...
, indicating that ''Monjurosuchus'' may have fed on invertebrates.[
]
Classification
''Monjurosuchus'' is a basal choristodere that lies outside the more advanced Neochoristodera
Neochoristodera is a lineage of specialised crocodile-like fully aquatic choristodere reptiles. Noted for their long jaws and large size, these animals were predominant across the Northern Hemisphere, occurring in freshwater and coastal environme ...
. When named in 1940, it was placed in its own family Monjurosuchidae. Unlike ''Monjurosuchus'', neochoristoderes have small, dorsally facing eyes and long snouts. ''Philydrosaurus
''Philydrosaurus'' is an extinct genus of choristoderan which existed in China during the Early Cretaceous. The type species ''P. proseilus'' was named in 2005. ''Philydrosaurus'' was found from the Jiufotang Formation and is slightly younger th ...
'', another Early Cretaceous Chinese choristodere, was grouped with ''Monjurosuchus'' in Monjurosuchidae. A 2007 phylogenetic analysis of choristoderes found only weak support for this family, as ''Philydrosaurus'' seemed to be a more basal choristodere than ''Monjurosuchus''. A close relationship was found between ''Monjurosuchus'' and the Miocene ''Lazarussuchus
''Lazarussuchus'' (meaning " Lazarus's crocodile") is an extinct genus of amphibious reptile, known from the Cenozoic of Europe. It is the youngest known member of Choristodera, an extinct order of aquatic reptiles that first appeared in the Midd ...
'', but this was only weakly supported.[
Phylogeny from the analysis of Dong and colleagues (2020):]
References
{{Taxonbar, from=Q3010132
Choristodera
Early Cretaceous reptiles of Asia
Yixian fauna
Prehistoric reptile genera